Study released by arXiv prepress server and already accepted for publication by Astrophysical Journal A report from NASA, based on 30 years of data from Hubble, which astronomers call “magnum opus(greatest work) of the space telescope. This data provides the most accurate measurement of the expansion rate of the universe.
The astronomical scientific community has known for more than a century that the universe is expanding, thanks to observations of the increasing distance between galaxies. The speed with which they are moving, relative to their distance from Earth, is called the “Hubble constant”, and measuring this value was one of the primary tasks of the space observatory.
To measure the Hubble constant, astronomers study distances to objects whose brightness is well known – so the fainter it looks, the further it goes. For relatively nearby objects within the Milky Way or in nearby galaxies, this role is filled by Cepheids, a class of stars that pulsate in a predictable pattern. For greater distances, scientists use the so-called Type Ia supernovae – cosmic explosions with well-defined peaks of brightness.
In recent decades, measurements of these objects have made it possible to calculate the Hubble constant at about 70 kilometers per second per megaparsec (/s/Mpc). Essentially, a megaparsec (about 3.3 million light-years) galaxy would be moving away from Earth at 70 kilometers per second, and that speed increases by 70 kilometers per second for every megaparsec away.
The Hubble Telescope provides the most comprehensive catalog of Cepheids and Ia supernovae.
For the new study, a team of scientists analyzed the most comprehensive catalog of these objects to date, to make the most accurate measurement of the Hubble constant to date. This was done by studying 42 galaxies that contain both apocalyptic and Type I supernovae.
“This is what the Hubble Space Telescope was built for, using the best technology we know,” said team leader Adam Rees, an astronomer at the Space Telescope Science Institute (Hubble and James Telescope Science Operations Center). Member of the National Academy of Sciences. “Maybe this is it magnum opus Hubble”.
Based on these surveys, the Hubble constant that the team calculated was 73.06 km/s/million segments. This reduces the margin of error to just 1.4%, which is a much more accurate measurement than previous measurements. This new precision could help astronomers improve models of cosmology, including better estimates of the age of the universe and what its future might hold.
However, there is still a great unknown. The Standard Model of cosmology predicts that the Hubble constant should be much slower – about 67.5 km/s/million segments. This was supported even by observations of background radiation left over from the Big Bang. The discrepancy appears to be related to the point in the universe we’re looking at – in our local area the constant is faster, while in the distant universe it’s slower, even after accounting for the known acceleration of expansion.
It might seem that the easiest explanation is that someone did something wrong, but oddly enough, both cases are pretty solid. Fortunately, we may not have to wait long to uncover new clues to the mystery, as James Webb will be able to study these same signs from greater distances and at a higher resolution than Hubble.
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